This invention relates generally to the exercise of control over and status monitoring of an operating system and is particularly directed to a microprocessor-based control/status monitoring arrangement for displaying control inputs and system status in a conventional electric power generating station.
The operation of an electric power generating station must be continuously monitored from a safety and economic standpoint in order to ensure early detection of potential problems so that corrective action may be implemented and the potential problem avoided. A typical electric power generating station utilizes hundreds of sensors to obtain on-line indications of operating parameters and further includes hundreds of control devices, e.g., pumps, valves, etc., for regulating operation of the power station. The control room of the power generating station provides the operators with a multiplicity of visual displays and indicators as well as aural alarms for apprising the station operators of the station's operating condition. Controls readily accessible to the operators are available for various of the aforementioned devices in exercising control over the power station.
One example of an indicator/control switch commonly used in conventional power generating stations is the mechanical memory, cam-operated control board switch. These cam-operated switches typically include a plurality of integral indicating lights as well as a rotatable handle connected to a rotatable shaft having positioned therein along its length a plurality of contact combinations and notched cams. The contacts are spring-loaded closed and mechanically opened by cam action to avoid sticking. Rotational displacement of the handle and shaft permits the operator to select various control inputs. The switch also typically includes a pull-to-lock mechanism to permit the operator to lock the switch into a given position. The small light bulbs and colored mechanical indicator disk on the front panel of the switch provide the operator with alarm and indicator lights as well as a visual indication of what the last active position of the switch was. The contacts are closed when the switch is turned to its commanded position, with the slip cams enabling the handle to return to normal without disturbing the slip-contact decks. The slip-contacts will only open when the switch is turned to another control position.
Power station operators have experienced various problems with these mechanical memory, cam-operated switches. For example, if the switch's handle is held too long in a given position, there is a possibility of damaging some of the control equipment. On the other hand, if the rotary handle is not held by the operator long enough in a given position, the desired control function will not be initiated. In the past, station operators have determined the optimum time to maintain the handle in a given position by trial and error and have attempted to introduce some reliability in the switch actuation process by relying upon the individual operator's "feel" for a given switch. This imprecise procedure has led to less than optimum results in power station control. In addition, when new control or status monitoring instrumentation is added, additional control switches must be provided for in the control panel. This frequently results in installation problems because of the limited space available and the requirement to mount these switches on either six- or three-inch centers. The mechanical memory, cam-operated switches also offer limited reliability particularly in the required high frequency replacement of burned out indicator bulbs. Finally, the use of these indicator bulbs limits the amount of information which can be displayed for an operator.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing a microprocessor-based control/status monitoring arrangement which makes use of a cathode ray tube (CRT) or other video display for presenting status information to an operator of an electric power generating plant and which also allows for the entry of control inputs in a user interactive manner. The control/status monitoring arrangement offers programmable flexibility to accommodate various combinations of sensors and control devices as well as to facilitate the incorporation of additional such devices without requiring additional space or electrical connections. While closely simulating the operation of prior art mechanical memory/cam operated control board switches, the present invention also offers the reliability of solid state electronics, the incorporation of additional status monitoring/control functions, and the flexibility of programming additional functions into the system, as well as establishing a hierarchy of selectable functions having various relative priorities.